The long term objective of the proposed research is to advance the understanding of how specific neuronal connections are established and maintained in the mammalian brain. This objective will be approached by studying the regulation and function of the clustered protocadherin (Pcdh) genes, which encode a family of cell surface proteins that localize to synaptic junctions. The unique organization of the Pcdh gene clusters, combined with cell-specific promoter activation and alternative pre-mRNA splicing, provides the potential for generating enormous protein diversity at the cell surface. This diversity could function as a molecular code for synaptic specificity. The regulation of Pcdh gene expression will be approached in two ways. First, regulatory proteins that bind to Pcdh promoters and intergenic regulatory DNA sequences will be identified and their functions determined through both in vivo and in vitro studies. The exciting possibility that these factors function in the coupling of transcription and splicing will be tested. Second, extra copies of well characterized Pcdh intergenic regulatory DNA sequences will be inserted into the Pcdh gene cluster to determine whether the limited number of Pcdh isoforms expressed from each chromosoome is a consequence of enhancer/promoter competition. Two approaches will be taken to determine the function of Pcdh proteins. First, Pcdh signaling pathways will be studied by identifying and characterizing the function of proteins that interact with Pcdhs in vivo and by identifying the genes they regulate. Second, mice bearing targeted mutations in the Pcdh gene clusters will be systematically characterized using histological and electrophysiological methods and behavioral paradigms. These studies should provide important new insights into the regulatory mechanisms for generating protein diversity in the brain, the function of Pcdh genes, and the pathological consequences of their loss of function. Interactions between neurons underlie normal brain function, and aberrant connectivity can lead to neurological and psychiatric disorders. A critical feature of brain function is the specificity of neuronal wiring. A better understanding of the mechanisms involved in this wiring may lead to a better understanding and treatment of mental illnesses, such as autism, schizophrenia and bipolar disease.